1. The Field of the Invention
The present invention relates to a conversion process starting with carbon fiber to produce partial metal carbide/carbon fibers and/or fully converted individual metal carbide fibers including calcium carbide, rare earth carbides, other metal carbides, and unique combinations of metal carbides, such as calcium carbide, rare earth carbides, other metal carbides, and optionally carbon (as an unreacted core) in a continuous or discontinuous fiber in a high purity form that is not obtainable using other processes today. More specifically, the invention, in various embodiments, relates to methods of producing metal carbides in continuous or other fiber forms, and articles including at least one or both of the continuous and/or discontinuous (chopped) metal carbide fibers and various weaves, braids and tubes of metal carbide fibers.
2. The Relevant Technology
There is a need today for economical metal carbide/carbon and metal carbide fibers as reinforcing fibers or as the base materials that in their respective current monolithic metal carbide form, have thousands of scientific and industrial uses. For example, lanthanide monolithic carbide compounds are used as catalysts in the production of petroleum and synthetic products. They are also used in lamps, lasers, magnets, phosphors, motion picture projectors, and X-ray intensifying screens. A pyrophoric mixed rare-earth alloy called Mischmetal (50% Ce, 25% La, 25% other light lanthanides) or misch metal is combined with iron to make flints for cigarette lighters. The addition of <1% Mischmetal or lanthanide silicides improves the strength and workability of low alloy steels. Several of the rare earths in current monolithic forms are also used in nuclear applications for their characteristic of high (Dy, Gd, Eu, Sin) or respectively low (Yb, La, Pr, Tb, Er, Tm) neutron cross section. In a continuous or chopped or milled fiber form, metal carbide fibers which are subjects of this invention can be woven into various forms for use in metal matrix composites, polymer matrix composites, and ceramic matrix composites having similar or compatible matrix such as silicon carbide, cerium carbide, hafnium carbide, etc.
Current metal carbides (MC) comprise or consist of chemically bonded metal (M) and carbon (C) atoms in a monolithic (non-fiber) form and exhibit beneficial properties, such as high hardness, high temperature stability, low electrical resistivity, and high resistance to corrosion and oxidation. Like diamond, a pure carbon compound, monolithic metal carbide compounds tend to be extremely hard, refractory and resistant to wear, corrosion, and heat. Due to these properties, monolithic metal carbides have current and potential uses in a palette of applications including coatings, rocket nozzles, optical coatings, electronic contacts, diffusion barriers, drill bits, and cutting tools. Other useful characteristics include a high temperature melting point, toughness, electrical conductivity, low thermal expansion and abrasiveness. Coatings of metal carbide have been formed on substrates by physical and chemical deposition techniques, such as pulsed laser deposition, reactive laser ablation, ultrahigh vacuum sputter deposition, high current plasma discharge arc deposition, co-evaporation, chemical vapor deposition, electron beam deposition, and ion beam assisted deposition applications including alloying agents with metals and ceramics, coatings for drills and other tools.
Currently, there are no known methods of forming metal carbides such as those contemplated herein, in fiber form, other than silicon carbide, boron carbide, and perhaps hafnium carbide and tantalum carbide. It would be an advancement in the art to provide metal carbides other than these carbides, in fiber form. It would be a further advancement if such could be provided through an economical process.